Calcium is a mineral essential in human nutrition and comprises approximately 1.5 to 2 percent of total adult body weight. Besides providing the skeletal structure for bones and teeth, calcium plays a key role in many other day-to-day functions of the body. Calcium is important for the normal clotting of blood, the conduction of nerve impulses, the contraction and relaxation of muscles as well as the regulation of body fluids, hormone secretion and cell division.
Calcium has received increased attention in dietary regimes in recent times because of its possible role in the prevention of diseases such as osteoporosis. The recommended daily allowance (RDA) for calcium is 1200 mg for women and 800 mg for men. Dairy products are considered an excellent source of calcium and the RDA is essentially met through the intake of dairy products.
Milk is a dairy product and as such a source of calcium. Milk generally contains 1200 mg per liter of calcium. However, as the demand for calcium has increased, it has become necessary to produce calcium fortified milk with a larger amount of calcium in a single serve.
A calcium fortified milk provides to people who do not choose to consume large amounts of dairy products an alternative to calcium mineral supplements.    Some Calcium fortified milk products use relatively insoluble forms of calcium such as tricalcium phosphate or calcium carbonate that have the disadvantage of having a gritty taste and sedimentation of the calcium salt. These forms of calcium require the use of suspension agents to maintain the calcium in suspension.    It has been observed that the addition of calcium salts to milk causes a drop in pH. This drop in pH is thought to be one reason for lack of heat stability in such calcium fortified milks where sedimentation occurs after pasteurisation. The raised calcium activity of milks with added calcium also contributes to heat instability. This has led some producers to add calcium after pasteurisation.
The specification of U.S. Pat. No. 5,449,523 discloses a process for the preparation of a calcium fortified yoghurt. The process includes the steps of mixing a fermentable dairy product with an alkaline agent, a chelating agent [preferably alkali metal citrates] and a source of soluble calcium. The alkaline agent and chelating agent are added to the mixture in amounts effective to maintain the pH of the yoghurt base mix above about 6.7. The yoghurt base mix is then pasteurised, cooled and inoculated with a yoghurt starter. The specification states that the invention is based on the unexpected discovery that the heat stability of yoghurt can be dramatically improved if the pH is not allowed to drop below about 6.7 prior to pasteurisation. Furthermore, a source of additional calcium can be added to the milk whilst maintaining the pH above 6.7 by adding a chelating agent and/or an alkaline agent at approximately the same time as the source of calcium in amounts effective to prevent the pH from dropping below 6.7. Experience has shown that milk stabilised with citrates and other chelating agents suffer from translucency apparently caused by migration of calcium from the protein micelles and release of casein into the serum.    Increasingly other nutritional minerals such as magnesium iron, zinc are being added to milk and milk products.    It is an object of this invention to provide heal: stable calcium and other nutritional mineral fortified milks that do not suffer any of the defects discussed above.    A further object of this invention is to produce calcium and other nutritional mineral fortified milk powders that have good heat stability when reprocessed after reconstitution.